Story-specific demand models and seismic fragility estimates for multi-story buildings

This paper develops seismic demand models for multi-story buildings. Story-specific demand models that consider the maximum interstory drift of each story are developed. Correlations among individual story demand models are also assessed to properly capture the potential dependence between maximum interstory drifts over the height of a building. Both linear and bilinear models in logarithmic space are considered to describe the relationships between drift demand and seismic intensity. A Bayesian approach is used to estimate the model parameters. The developed demand models are used to estimate the seismic fragility of two example buildings. The fragility estimates are compared with currently available estimates based on demand models for the overall maximum interstory drift. It is shown that when only the maximum interstory drift of a building is considered, the fragility might be underestimated; particularly if the interstory drifts for one or more stories are close to the maximum value. The proposed methodology provides a refined approach that includes more building response information than typical demand models, allowing for more accurate estimates of the seismic fragility of multi-story buildings.